The area of a circle is defined as πr^2. Estimate π to 3 decimal places using a Monte Carlo method. Hint: The basic equation of a circle is x2 + y2 = r2.

daily-coding-problem-14.rb

#!/usr/bin/env ruby

def pi_estimation(r=5)
    inside =0.0
    outside = 0.0
    total = 0.0
    rnd = Random.new

    for i in 1 ... 10000
        x = rnd.rand(-1*inside..inside)
        y = rnd.rand(-1*inside..inside)

        measure = distance(x, y)
        if measure > inside
            outside += 1
        else
            inside += 1
        end 
    end
    total = outside + inside
    return  (4 * (inside / total)).to_f()
end 

def distance(x1, y1, x=0, y=0)
    x_diff = x1 - x 
    y_diff = y1 - y 
    x_diff *= x_diff 
    y_diff *= y_diff 
    return Math.sqrt(x_diff + y_diff)
end 

puts '%.2f' % pi_estimation()